"Even though it is a culture, and it's a cultural thing, he goes in, he takes over, he's the boss. It's incredible."
Trump stressed Kim's strength to take tough decisions at young age like executing top generals including his own uncle.
"You've got to give him credit," Mr Trump said. "How many young guys — he was like 26 or 25 when his father died — take over these tough generals, and all of a sudden — you know, it's pretty amazing when you think of it. How does he do that?
The billionaire seems to be impressed by the North Korean leader's ways demonstrating possession of a nuclear bomb meaning he takes him very seriously.
"He wiped out the uncle, he wiped out this one, that one. This guy doesn't play games and we can't play games with him. Because he really does have missiles and he really does have nukes."
In December, Kim Jong-un said the country possessed a hydrogen bomb and was ready to use it to "protect its sovereignty and national dignity."
North Korea declared itself a nuclear power in 2005, and has conducted at least three underground nuclear weapon tests since then, raising concerns both in the neighboring states and worldwide.